The Thanedd coup occurred during a planned mages' reunion on the island. The banquet preceding the reunion began quietly enough with mages discussing their alliances with either the Northern Kingdoms or Nilfgaard, or professing neutrality but things soon began to heat up.
Mages employed by Nilfgaard, led by Vilgefortz, had planned a sneak attack on their northern counterparts. The Northern supporters caught wind of the treachery and quietly tried to restrain the enemy mages before the plan could be executed, with the help of Dijkstra and his men. However, when Yennefer brought Ciri, and she revealed violent events occurring in the North, like King Vizimir's assassination and Demavend's preemptive strike on Nifgaard, Tissaia de Vries removed the anti-magic barrier in the area, leading to an all out battle between the mages. The entrance from the interior of the hollow island to Garstang was opened by Francesca Findabair, revealing a large unit of Scoia'tael commandos who had been secretly transported to the island to take part in the coup by Cahir Mawr Dyffryn aep Ceallach, Rience, and Faoiltiarna.
Yennefer had brought Ciri to the proceedings and Cahir and Rience had hoped to capture the girl there. Cahir nearly did, but Ciri was able to defeat him in a sword fight and flee. Geralt nearly killed Cahir as well, but relented at the last moment when the knight revealed that he had been the one who had saved Ciri during the Slaughter of Cintra.
At the end of the skirmish, Geralt then met and fought Vilgefortz but the mage was far more skillful than the witcher had anticipated. Vilgefortz seriously wounded Geralt, but did not kill him (although he easily could have). Instead, the mage told him that this encounter had been a "little lesson" and then fled, presumably still trying to get Ciri. Triss Merigold then found the witcher and transported him to Brokilon with the help of Tissaia de Vries.
Fatalities of the coup Edit
Following the coup, confidence in mages seriously declined and many of them were expelled from the royal courts. It is also cited as one of the precipitating events of the war that followed. For her role in the coup, Francesca Findabair was made queen of Dol Blathanna, a free elven state, under the condition that she would openly denounce the violent actions of the Scoia'tael, while allowing them to continue to harass the Northern Kingdoms. The fall of the Council and Chapter of Sorcerers led to Philippa and other sorceresses forming the Lodge of Sorceresses.